Ball screw and nut combination

ABSTRACT

A ball screw and nut combination in which the nut is essentially cylindrical in configuration, is provided with internal threads and a plurality of openings extending generally tangentially into a thread groove and communicating with a helically formed groove or recess at the exterior in helical alignment with but spaced by a smooth cylindrical uninterrupted exterior surface of the nut from a similar helical groove communicating with a second opening communicating tangentially with a thread groove. A cover of sheet material such as metal or plastic is attached overlying the openings and helically extending grooves or channels, the cover having a helically extending groove communicating with said openings and recesses or channels and the smooth exterior surface of the nut to define an enclosed ball return passage interconnecting the openings.

United States Patent Gagne 51 May 9,1972

[54] BALL SCREW AND NUT COMBINATION [72] Inventor:

[73} Assignee: Precise Services, Inc., Detroit, Mich.

[221 Filed: May 18, 1970 [21] Appl. No.: 38,454

Oscar J. Gagne, Grosse Pointe, Mich.

52 user ..74/459 511 1nt.Cl ..rusnssno 5s] FieldofSearch ..74/459,424.s

[56] References Cited UNITED STATES PATENTS Prueter ..74/459 X Galonskaet al. ..74/459 5 7] ABSTRACT A ball screw and nut combination in whichthe nut is essentially cylindrical in configuration, is provided withinternal threads and a plurality of openings extending generallytangentially into a thread groove and communicating with a helicallyformed groove or recess at the exterior in helical alignment with butspaced by a smooth cylindrical uninterrupted exterior surface of the nutfrom a similar helical groove communicating with a second openingcommunicating tangentially with a thread groove. A cover of sheetmaterial such as metal or plastic is attached overlying the openings andhelically extending grooves or channels, the cover having a helicallyextending groove communicating with said openings and recesses orchannels and the smooth exterior surface of the nut to define anenclosed ball return passage interconnecting the openings.

5 Claims, 7 Drawing Figures PATENTEDMAY 91972 1 3,661,030

sum 1 OF 2 INVENT ATTORNEYS ojzm J. AG BY Z 4 I PATENTEDMAY 9 I972 3,661 030 SHEET 2 0F 2 FIG. 4

FIG. 5

FIG.6

' INVENTOR 05.; R GAGNE ATTORNF.

BRIEF SUMMARY OF THE INVENTION The ball screw and nut combinationcomprises a screw of usual configuration having a helically extendingball receiving groove. Associated with the screw and relatively movablelongitudinally thereof upon relative rotation therebetween is a nut ofspecial design. Essentially, the nut comprises a cylindrical body whichmay at one end have an externally threaded extension for connection to adevice to be moved longitudinally of the screw. The nut is provided withone or more ball return passages and these passages include openingswhich communicate substantially tangentially with thread grooves formedat the interior of the nut body. Each of the openings is incommunication with a helically extending groove or channel which extendstoward but is spaced from a cooperating groove or channel which in turncommunicates with another opening extending generally tangentially intoan internal thread groove in the nut. Accordingly, each of the groovesor channels which connects to an opening is of diminishing depth andruns out so that a smooth uninterrupted cylindrical surface area at theexternal surface of the nut lies between the adjacent ends ofcommunicating grooves or channels.

The ball return passage is completed by a generally partiallycylindrical relatively thin plastic cover which is deformed to provideinternal grooves or channels adapted to interconnect a cooperating pairof openings and to overlie the helically extending grooves or channelsat the exterior of the nut body. Accordingly, the helically extendinggrooves or channels associated with a cooperating pair of openings inthe nut body and the grooved portion of the cover define a helicallyextending ball return passage, a substantially intermediate portion ofwhich is formed by the smooth uninterrupted exterior surface of the nutbody.

Ball deflecting elements are provided which include a helicallyextending bar adapted to be received in a short portion of a threadgroove in the nut body and to occupy a corresponding portion of themating thread on the screw. The end surfaces of the helical bar areconcavely formed and are positioned to form extensions of the openingsthrough the nut which extend generally tangentially into the threadgrooves. The arrangement is such that as a ball is caused to roll aroundthe thread groove of the nut, it eventually engages one end of thehelical bar and is forced through the tangential opening into the ballpassage along which it is advanced and eventually caused to re-enter theball nut through the associated opening.

Each of the helical bars includes a generally radially extending stemhaving at its end a head spaced from the stem by an annular groove. Thestem extends through a radial opening in the nut body and through anopening in the plastic cover. Suitable means such for example as aU-shaped or C-shaped clip engages in the annular groove beneath the headof the stem and serves to retain the bar and the plastic cover in place.

Preferably, each nut includes a pair of cooperating openings and theplastic cover is accordingly provided with a pair of generally helicallyextending channels. With such an arrangement, three helical bars areprovided, the intermediate bar serving as a ball abutment to deflectballs into either of the ball return passages, depending upon thedirection of relative rotation between the ball nut and screw.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the assemblyof the ball nut and screw.

FIG. 2 is a section on the line 2-2, FIG. 1.

FIG. 3 is a sectional view on the line 33, FIG. 1.

FIG. 4 is a plan view of a portion of the nut with the cover removed.

FIG. 5 is a plan view of the ball deflector.

FIG. 6 is an elevational view of the ball deflector.

FIG. 7 is a fragmentary section on the line 77, FIG. 1.

DETAILED DESCRIPTION Referring now to FIG. 1, the ball screw shaft isindicated at 10 and is provided with a generally arcuate thread groove12 which extends helically of the screw. The ball nut is indicatedgenerally at 14 and comprises a body which is of generally cylindricalconfiguration. At one end the body has a threaded extension 16 separatedfrom the nut proper by an external annular groove 18. The threadedextension 16 is for connection of the nut to structure which is adaptedto be moved relatively longitudinally of the screw.

At its interior surface the nut is provided with a helically extendingthread groove 20 which is in matching relation and associated with theexternal thread groove 12 of the nut so as to define a ball receivingpassage indicated generally at 22, suitably dimensioned with respect tothe balls 24 so that the balls have rolling contact with cooperatingthread surfaces as the nut and screw are relatively rotated.

Means are provided for deflecting the balls to move outwardly of the nutand to return them to a new position as relative rotation continues.Thus, the balls in effect circulate in an endless passage, a portion ofwhich is a helix of several turns defined by the confronting threadgroove portions of the nut and screw. The remainder of the circulatingpassage is the return passage which receives balls from the threadpassage and returns them externally of the nut to the thread passage tobegin their movement along the thread configuration of the ball and nut.

For this purpose and as best seen in FIG. 2, the nut 14 is provided withopenings 26 which extend generally tangentially into the thread grooveformed in the nut body. Each of the openings 26 is in communication witha groove or channel 28 which intersects the tangential opening 26 andwhich diminishes in depth until it terminates or runs out into thesmooth cylindrical surface at the exterior of the nut as indicated at30.

Associated with the nut 14 is a cover 32 preferably formed of plasticmaterial having a thickness such that it may be readily deformed intothe configuration illustrated in the drawings. The shell or cover 32,generally cylindrically formed having for example an annular extent ofapproximately is adapted to overlie the tangential openings 26 formed inthe nut body.

The cover is provided with deformed grooves or channels 34 whichcooperate with the openings 26 and the grooves or channels 28 formed inthe exterior surface of the nut 14. The grooves or channels 34 in thecover taper in depth at their ends as clearly indicated by the referencecharacter 36 and this decrease in depth in effect matches the variabledepth of the grooves or channels 28 so that the surfaces of the externalgrooves or channels 28 in the nut body and the interior surfaces of thegrooves or channels 36 in the cover 32 define substantially enclosedcontinuous ball passages. The intermediate portion of the ball passages,as best illustrated in FIG. 7, comprises a portion of the smoothcylindrical exterior surface of the nut body as indicated in this Figureat 38 and also clearly indicated in FIG. 4.

In order to deflect the balls as they move around the ball receivingpassage 22 and to retain the cover 32 in properly assembled position,ball deflectors, best illustrated in FIGS. 5 and 6, are provided. Eachof these ball deflectors comprises a short helical bar portion 40 ofgenerally circular cross-section and adapted to be received in a portionof the thread groove of the nut and to extend into the cooperatingportion of the thread provided in the screw. The helical bars 40 arecylindrically recessed at their ends as indicated at 42 to providesurfaces which cooperate with portions of the surfaces of the openings26 to define generally tangential ball guide passages as best indicatedin FIG. 2. Each of the bar portions 40 carries a stem 44 which isadapted to extend through a radial opening 46 in the nut body. Similaror matching openings are provided in the cover 32 as best indicated inFIG. 2. The stem 44 includes an annular groove 47 positioned below anexternal head 48 which is adapted to extend through the opening in thecover and to retain the cover in position in association with a C-clampor U-clamp 50.

As best illustrated in FIGS. 1 and 4, a ball nut designed to have twoball circulating paths therein is provided with three of the radialopenings 46 each of which receives a stud or stem 48 of a balldeflector.

It will be apparent from FIG. 2, which is a sectional view along asingle thread, that the ball deflector bar 40 is adapted to engage ballsmoving clockwise of the assembly at its left hand end and to cause theseballs to move outwardly through the opening designated 26 in FIG. 2 andto cause these balls to traverse the ball passage which includes thechannel portion 34a of the cover to the tangential opening 26!: at whichpoint the balls again enter into cooperation between the confrontingball receiving thread portions of the nut and screw. Upon reverserelative rotation between the screw and nut, the balls engage theopposite end of the ball receiving portion and are deflected outwardlyand pass in the opposite direction through the ball passage defined inpart by the groove or channel 34 formed in the cover and in part by thehelical grooves or passages 28 formed at the exterior of the nut body.

The present construction represents an advance over prior known ball nutand screw combinations in several particulars. In the first place, theuse of the plastic cover which cooperates with grooves or channels inthe exterior of the cylindrical nut body to form ball return passagesprovides extremely quiet operation and protects the balls against wearor damage as they are circulated in a return flow. Secondly, the helicalconfiguration of the ball return passage resulting from the helicalconfiguration of the channel or groove portions provided at the interiorof the cover and at the exterior of the nut body, provides for the mostefficient flow of balls as they return for reuse from the exit passageto the reentrance passage into the ball nut.

In addition, since grooves or recesses 28 terminate or run out into thesmooth cylindrical surface of the nut body, a portion of the ball returnpassage is defined by this surface. This simplifies the construction andprovides maximum economy in producing the nut, since it is formed bysimple machining operations, starting from ordinary tubular stock.

The use of the ball deflectors with headed stems for association withC-clamps or U-clamps provides for extremely effcient assembly and at thesame time for accurate location of the external cover in the positionrequired for most efficient cooperation with the ball return grooves atthe exterior of the ball nut.

Whatl claim as my invention is:

1. A ball nut for association with an elongated ball screw, said nutbeing generally of cylindrical configuration provided with an internalball receiving thread groove, said nut having at least a pair ofopenings extending from its exterior surface in substantially tangentialrelation to the internal thread groove, the exterior surface of said nuthaving inclined grooves of variable depth, each of said grooves being incommunication with one of said openings and extending toward butterminating short of a similar inclined groove communicating with thesecond opening of the pair, a cover plate overlying a portion of thecylindrical exterior surface of said nut and having an internal grooveof variable depth communicating with the pair of grooves formed in theexterior surface of said nut to define therewith and with the smoothuninterrupted cylindrical surface portion of the nut a continuous ballreturn passage.

2. A nut as defined in claim 1 in which a plurality of pairs of openingsare provided in the nut and a corresponding number of internal groovesare provided at the interior surface of the cover.

3. A nut as defined in claim 1 in which the cover is formed of a thinshell of uniform thickness of plastic material deformed to the requiredconfiguration to provide the internal gmoves- 4. A nut as defined inclaim 3 1n WhlCh said plastic shell, ex-

cept for the portions deformed into the aforesaid grooves, is ofgenerally cylindrical configuration and is adapted to be retained inclose surface-to-surface relationship with the smooth exteriorcylindrical surface of the nut.

5. A nut as defined in claim 4 in which the nut body has a generallyradial opening extending into a thread groove at the interior of thenut, a ball deflector having a helically extending bar partiallyreceived in the thread groove in the nut, said bar having a sternextending through the radial opening and through an opening in saidcover, and means retaining the stern against inward movement of theopening to retain the deflector bar in position and to retain said coveron said nut.

1. A ball nut for association with an elongated ball screw, said nutbeing generally of cylindrical configuration provided with an internalball receiving thread groove, said nut having at least a pair ofopenings extending from its exterior surface in substantially tangentialrelation to the internal thread groove, the exterior surface of said nuthaving inclined grooves of variable depth, each of said grooves being incommunication with one of said openings and extending toward butterminating short of a similar inclined groove communicating with thesecond opening of the pair, a cover plate overlying a portion of thecylindrical exterior surface of said nut and having an internal grooveof variable depth communicating with the pair of grooves formed in theexterior surface of said nut to define therewith and with the smoothuninterrupted cylindrical surface portion of the nut a continuous ballreturn passage.
 2. A nut as defined in claim 1 in which a plurality ofpairs of openings are provided in the nut and a corresponding number ofinternal grooves are provided at the interior surface of the cover.
 3. Anut as defined in claim 1 in which the cover is formed of a thin shellof uniform thickness of plastic material deformed to the requiredconfiguration to provide the internal grooves.
 4. A nut as defined inclaim 3 in which said plastic shell, except for the portions deformedinto the aforesaid grooves, is of generally cylindrical configurationand is adapted to be retained in close surface-to-surface relationshipwith the smooth exterior cylindrical surface of the nut.
 5. A nut asdefined in claim 4 in which the nut body has a generally radial openingextending into a thread groove at the interior of the nut, a balldeflector having a helically extending bar partially received in thethread groove in the nut, said bar having a stem extending through theradial opening and through an opening in said cover, and means retainingthe stem against inward movement of the opening to retain the deflectorbar in position and to retain said cover on said nut.